android - RecycleView 在 Fragment 中崩溃，因为 LayoutManager 为 NULL

Question

我有三个标签，它们都在一个 tablayout 中，在 Tab1 中，有一个 RecycleView。

今天想给它加上SwipeRefreshLayout:

<android.support.v4.widget.SwipeRefreshLayout
    android:id="@+id/swiperefreshlayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </android.support.v7.widget.RecyclerView>

</android.support.v4.widget.SwipeRefreshLayout>

在 Tab1Fragment 中:

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.activity_main_list, container, false);
    recyclerView = (RecyclerView) view.findViewById(R.id.recyclerView);
    staggeredGridLayoutManager = new StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.VERTICAL);
    recyclerView.setLayoutManager(staggeredGridLayoutManager); 
    swipeRefreshLayout = (SwipeRefreshLayout) view.findViewById(R.id.swiperefreshlayout);
    swipeRefreshLayout.setColorSchemeResources(android.R.color.holo_blue_bright, android.R.color.holo_green_light,
            android.R.color.holo_orange_light, android.R.color.holo_red_light);
    return view;
}

不幸的是，当我从 tab1 滚动到 tab2，然后返回到 tab1 时， Activity 崩溃了:

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean  
android.support.v7.widget.RecyclerView$LayoutManager.canScrollVertically()' on a null object reference
  at android.support.v7.widget.RecyclerView.computeVerticalScrollOffset(RecyclerView.java:1613)
  at android.view.View.canScrollVertically(View.java:12880)

但显然我设置了 LayoutManger!看起来交错的网格布局不见了......

更奇怪的是，当我只点击tab1、tab2时，Activity没有崩溃，但是当我从tab2滚动到tab1时，它崩溃了

发生了什么事？谢谢!

加上整个错误日志:

12-02 16:57:59.857 28189-28189/xyz.doutu.doutu E/AndroidRuntime: Process: xyz.doutu.doutu, PID: 28189
        ava.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.support.v7.widget.RecyclerView$LayoutManager.canScrollVertically()' on a null object reference
  at android.support.v7.widget.RecyclerView.computeVerticalScrollOffset(RecyclerView.java:1613)
  at android.view.View.canScrollVertically(View.java:12880)
  at android.support.v4.view.ViewCompatICS.canScrollVertically(ViewCompatICS.java:35)
  at android.support.v4.view.ViewCompat$ICSViewCompatImpl.canScrollVertically(ViewCompat.java:1253)
  at android.support.v4.view.ViewCompat.canScrollVertically(ViewCompat.java:1695)
  at android.support.v4.widget.SwipeRefreshLayout.canChildScrollUp(SwipeRefreshLayout.java:646)
  at android.support.v4.widget.SwipeRefreshLayout.onInterceptTouchEvent(SwipeRefreshLayout.java:660)
  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:1961)
  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2408)
  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2050)
  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2408)
  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2050)
  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2408)
  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2050)
  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2408)
  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2050)
  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2408)
  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2050)
  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2408)
  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2050)
  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2408)
  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2050)
  at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2408)
  at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2050)
  at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchTouchEvent(PhoneWindow.java:2390)
  at com.android.internal.policy.impl.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1734)
  at android.app.Activity.dispatchTouchEvent(Activity.java:2833)
  at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:60)
  at android.support.v7.view.WindowCallbackWrapper.dispatchTouchEvent(WindowCallbackWrapper.java:60)
  at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:2351)
  at android.view.View.dispatchPointerEvent(View.java:8700)

Answer 1

将您的 recyclerView 分配移动到 onViewCreated() 而不是 onCreateView()。问题是当您的 TabFragment 分离并重新附加到 viewPager 滚动条上时。